Edge sensing apparatus

ABSTRACT

Apparatus for detecting the presence of a web material at a given location, including a movable member at the location, having a conduit therethrough, and pressure fluid means cooperating with the movable member for discharging through the conduit when no web material is present at said location and for building up pressure behind the movable member, for urging the latter against the web material when the web material is present at said location. Sensing means cooperate with said fluid pressure means for detecting such build up of pressure.

Apr. 17, 1973 United States Patent [191 Tibavido EDGE SENSING APPARATUS [75] Inventor: Raymond S. Tibavido, Seaford, NY. Primary Examiner Richard Schacher Attorney-Henry Stemberg Leigh Systems, Inc., Syracuse, NY.

Jan. 12, 1972 Assignee:

Apparatus for detecting the presence of a web materi- ABSTRACT [22] Filed:

Appl. No.: 217,329

al at a given location, including a movable member at the location, having a conduit therethrough, and sure fluid means cooperating with the mo presvable member for discharging through the conduit when no web material is present at said location and for build- 2 m 2 6 m a 2 W 2 9 "2 H 6 "m 2 u m" m L hf C l0 WM t e U .mh l ll. 2 8 5 55 ll.

ing up pressure behind the movable member, for urging the latter against the web material when the web material is present at said location. Sensing means cooperate with said fluid pressure means for detectin such build up of pressure.

UNITED STATES PATENTS 3,07l,l5 7 v l/l963 Robertson 226/23 3/1965 Robertson.....'...........i.............226/23 12 Claims, 4 Drawing Figures fi e-saute: 110

PATENTED APR 1 H975 SHEET 1 OF 3 BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to apparatus for detecting the presence of sheet material at a given location and more specifically for detecting transverse displacement of a longitudinal edge of a longitudinally moving web of sheet material such as, for example, paper.

In the manufacture or processing of sheet material, particularly paper, it is often desirable and frequently necessary to maintain a longitudinal edge of the web moving along a predetermined longitudinal path', or to mark or otherwise indicate movement of the edge out of such path. In order to accomplish this it is necessary to detect transverse shifting of the web edge out of such path.

2. Description of the Prior Art While a sensing device which physically contacts the edge of the moving web material would be most advantageous from the point of view of reliability, most of the known devices which rely onphysical contact to signal a shift of the edge of the web are not suitable for use with delicate materials such as paper. In these known devices the contacting member is under a load sufficient to insure a positive signal when engaged by a web material. This is not suitable for delicate material such as paper, however, because of the susceptibility of such materials to tearing and/or similar damage when the edge of a fast moving web makes sufficient physical contact with a loaded sensing member to overcome such loading in order for a signal to be produced. Thus, because of the delicate nature of paper, particularly the edge portion of a fast moving web of paper, it has in the past appeared highly desirable to avoid use of sensors which rely on direct physical contact with the paper web.

Devices which do not rely on physical contact generally comprise pneumatic systems where, for example, air under pressure is directed from a nozzle into an opening located adjacent the edge of the web. A pressure sensor communicates with this opening and when the web shifts to a position where its edge intercepts the stream of air the resulting blockage is detected by the pressure sensor. A disadvantage of the latter system is that the opening into which the air stream is directed is necessarily of relatively small size and therefore easily clogged, particularly by the large amounts of contaminants in the atmosphere of a paper mill. This frequently results in an erroneous signal.

Known devices which do not use physical contact but rely entirely on pneumatic means are illustrated in U. S. Pat. No. 3,194,055 (Knobel) and US. Pat. No; 3,025,696 (M atteson), in each of which a nozzle directs a streamof air against the surface of a web. The nozzle is movable toward and away from the web surface to always maintain a fixed spacing between it and such surface. Back pressure in the nozzle supply conduit builds up when an additional layer' of the web material enters the region toward which the air jet is directed, for moving the nozzle away from the web material by a distance equal to the thickness of the added web layer in order to maintain always a fixed spacing between the nozzle and the surface against which the jet is directed. This movement of the nozzle is sensed and used to provide a signal. Where relatively thin sheet material, such as paper. is to be detected,

devices of the latter type become relatively complicated and expensive.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the aforesaid disadvantages of the known sensing devices.

It is a further object of the present invention to provide a web edge sensing apparatus which is relatively inexpensive and relatively free of maintenance problems.

It is still another object of the present invention to provide an edge sensing apparatus suitable for use with delicate web materials, such as paper, for reliably detecting transverse movement of a longitudinal edge of such web.

It is still another object of the present invention to provide a web edge sensing apparatus such as described above which will reliably operate with web materials of varying thickness and which will automatically adjust itself to such varying thicknesses.

Another object of the present invention is to provide an apparatus such as described above which will not mar or otherwise injure a paper web moving at high speed.

A further object is to provide apparatus of the above type which is adapted to be readily installed on or removed from a web processing or manufacturing line.

A still further object is to provide apparatus of the above type which is readily adaptable to various control and/or indicating functions.

A concomitant object is to provide apparatus of the above character which is substantially insensitive to variations in most of the parameters of the system, and which responds primarily only to lateral shifting of the web edge.

According to the present invention there is provided a novel combination of a pneumatic system and a movable feeler member which permits the feeler member to make initialphysical contact with the edge of the moving web material while being subjected to only very light loads,not sufficient to damage the web, even when such may be a delicate material as paper, yet capable of positive sensing of web edge position. The pheumatic system cooperates with the movable feeler member by exhausting to atmosphere when no web material is present under the feeler member and by building up pressure behind the movable feeler member, for urging the latter against the surface of the web material, when web material is present under the feeler member, so as to further increase the built-up pressure only after the feeler member is already on the surface of the web material, and for detecting such build-up of pressure.

Accordingto'the preferred embodiment of the invention there is provided a movable feeler, or plunger member, having a first portion extending into the horizontal path along which the edge of the moving web may shift. The plunger is slidably received in a chamber so as to be freely movable in a generally vertical direction, out of the plane of movement of the web, in response to contact of the first portion of the plunger by an edge of the web when the latter shifts toward the plunger. An air passage extends through the .plunger and has an outlet opening which is uncovered when the web is not in the region beneath the plunger and which is covered by the surface of the web, when the web is beneath the plunger. When the outlet opening of the plunger is covered by the web, air which was previously exhausted to atmosphere through the outlet opening is blocked, resulting in a build-up of back pressure behind the plunger. This built-up back pressure urges the plunger in a direction toward the web surface on which the plunger is resting, thereby even more tightly sealing the plunger outlet opening against such surface. The build-up in back pressure is sensed by pressure sensing means which, through suitable control means, may provide either an indication to an operator that the web edge has laterally shifted out of its prescribed path or a signal to a suitable control means for automatically shifting the web laterally in a direction to return the web edge to its prescribed path, or a signal to a suitable marking device for marking the web at such locations therealong at which the edge is in shifted position.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and the entire scope of the invention will become more fully apparent when considered in the light of the following detailed description of the illustrative embodiments of this invention and from the appended claims. The illustrative embodiment may be best understood by reference to the accompanying drawings, wherein:

FIG. 1 is a schematic, perspective, view of a web edge sensing apparatus,according to the preferred embodiment of the present invention,flxed to a conveying table adjacent the edge of a moving web and showing diagramatically a shifting means and a control means for laterally shifting the moving web in response to signals generated by said sensing apparatus;

FIG. 2 is a schematic view, partly to enlarged scale and partly broken away, of a portion of the web edge sensing apparatus shown in FIG. 1;

FIG. 3 is an enlarged perspective view of the sensing head shown in FIG. 2; and

FIG. 4 is a partial, partly sectional, partly schematic view of the sensing apparatus of FIG. 3, having a pair of cooperating plunger members and web guide means therefor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS adapted to generate suitable electrical signals. The

electrical outputs of 40 and 40 are transmitted, via suitable circuits 4,4, to control means 5 and 5' respectively. These actuate web shifting means 35 suitable connected to web support roll R for shifting the web W,

in response to said signals, to return the edge W to said given path P. Alternatively, the signals produced by the control means 5, 5' may be used to operate a simple sensitive relay to shut down the process, give a suitable alarm, or activate a marking device for'marking the web at such location therealong where the edge deviated from its given path.

According to the preferred embodiment the sensing head 1 (FIG. 4) includes a pair of identical feeler members, or plungers, 10 and 10 each axially slidable in chambers 20 and 20', respectively, provided in the upper arm 31 of a support member 30. It will be understood however that the invention can also be practiced with only a single plunger (FIG. 2), as will now be described. Since the plungers 10 and 10', the chambers 20 and 20' and the pneumatic systems 40 and 40, respectively associated therewith in the two plunger system (FIG. 4) are identical in all respects, only a one plunger system need be described in detail.

The plunger 10 is preferably cylindrical and has a flat head portion 12 at the upper axial end thereof and a flat bottom surface 14 at the lower axial end thereof. A bore 15 extends through the plunger 10 from the top to the bottom surfaces thereof preferably spaced from but parallel to the axis thereof. The chamber 20 is preferably vertically oriented and open downwardly. The head end of plunger 10 is received in bore 20, while the lower end portion 14 thereof normally extends out of the chamber and into a space S formed between an upper arm 31 and a lower arm 32 of support 30. Thus the plunger 10 normally rests with its bottom surface 14 in fact-to-face contact with the top surface 33 of lower arm 32. Directly opposite the bore 15 of the plunger and coaxial with such bore there is provided, in the lower arm 32, an air passage 34, preferably of substantially the same cross sectional area as the bore 15. The depth of chamber 20 is such that in all operating positions of the plunger 10 there will always be a space 22 between the top surface 12 of the plunger and the closed end wall 21 of the chamber. An inlet passage 24 communicating with a pressure fluid system 40 opens into the space 22 near the top end wall 23. System 40 includes a source of air, or other suitable pressure fluid, 41, a conduit bridge means 42, and a differential pressure sensing means 44. Conduit bridge 42 includes a pair of conduit legs 52, and 52a, connecting opposite sides of said differential pressure sensing means 44 to intermediate portions 51 and 51a, respectively, of conduit legs 50 and 50a.

Plunger 10 is formed, at its lower end, with an inclined surface portion 16 constituting an actuating means for lifting the plunger onto the surface of a web W as the web passes thereunder. Thus, when the edge W of the web material enters slot S and shifts laterally along the surface 33 toward plunger 10 it will first contact the inclined surface portion 16 of the plunger and lift the latter, by pushing against portion 16, onto the web surface to the position seen in FIG. 2. It is preferable to key the cylindrical plunger 10 with respect to the bore 20 so that the inclined surface 16 thereof will always face in the direction in which a leading edge W of the web will approach.

The fit between plunger 10 and its chamber 20, is such as to permit free axial sliding movement of the plunger within the chamber. It is an advantage of the present invention that it is not necessary to take special precautions to prevent escape of pressure fluid between the plunger and the chamber in which it is slidably received. It is therefore'possible to minimize the frictional resistance which a .delicate web must overcome in lifting the plunger from its rest position (plunger in FIG. 4) to its actuated position (plunger 11) in FIG. 4).

Conduit bridge means 42 defines two paths between the pressurized air source 41 and the atmosphere. Namely, a first, or reference, path in which air from supply 41 flows through leg 50 directly to the outlet 53 where it is discharged to the atmosphere, and a second, or monitoring, path where air from supply 41 flows serially through the conduit leg 50,, coupling 25, inlet conduit 24, chamber 22, bore and (if no web were present under the plunger 10) thence through the passage 34 to discharge to the atmosphere.

The differential pressure sensing means 44 which communicates, via conduits 52 and 52,, with an intermediate region 51, of conduit 50,, in the monitoring path and with an intermediate region 51 of conduit 50 in reference path, is capable of detecting a predetermined unbalance in pressure between the monitoring path and the reference path.

In rest position, i.e., with no web present, the bottom surface 14 of plunger 10 rest flush against the surface 33. In this condition, pressure fluid from the source 41, flows along both the monitoring and reference paths to be exhausted freely to the atmosphere via the outlet 53 of the reference path and via the bore 34 of the monitoring path.

Thus, when no web is present under plunger 10, exit to the atmosphere of fluid passing through the internal passage 15 is not blocked and the system 40 will be in substantial balance. Whatever unbalance does result from system configuration can be compensated for by suitable adjustment of the pressure sensor 44. When, however, the flow through passage 15 of the plunger 10 is blocked by the presence of a web covering the outlet opening 19 thereof (FIG. 2), the pressure sensor 44 will detect the resultant imbalance and develop a suitable output signal.

According to the preferred embodiment of the present invention, upper and lower arms 31 and 32 comprise a pair of closely adjacent, but spaced, straight portions 31a and 32a, respectively connected at corresponding ends thereof to a main support member 36 adapted to be suitably mounted on a conveying table, or the like, along the path of the edge W of the web conveyed thereon. Arms 31 and 32 preferably extend in a direction transverse to the direction of advance A of the web W and have free end portions 31a and 32a extending away from one another to form a guide means having a V-shaped mouth opening toward the web in the direction B for guiding the edge W,, of the web into the space S formed between the spaced straight portions 31a and 32a of the arms.

A second guide means comprises a pair of oppositely inclined members 31a" and 32a" fixed, respectively, to the arms 31 and 32. Members 31a" and 32a" extend substantially parallel to the direction of web advance A and together from a V-shaped mouth opening in a direction opposite to the direction of advance A of the web. Member 36 is adapted to be rigidly connected to a table 2, while arms 31 and 32 are preferably adjustably supported by members 36, so as to permit the arms to be shifted vertically with respect to one another for increasing or decreasing the thickness of slot S defined therebetween.

A single plunger with its associated pneumatic system as described above, is suitable, for example, where it is desired to detect the presence or absence of web material at a given location or to sense the arrival of a web edge at a given location. The signal generated by the pressure sensor 44, when a predetermined imbalance is sensed, may be transmitted through suitable circuitry 4 to an actuating device which may either generate a warning signal such as for example an audible signal indicating that the edge W of the web has shifted transversely or it may generate a signal suitable for a web positioning means adapted to automatically shift the web material laterally in a direction opposite to the one in which it initially shifted, to return the edge W L of the web toward its desired path. Where however, it is desired to sense a shift of the web edge, in either direction, away from the desired path, such as where, e.g., it is desired to maintain the edge of a web material substantially along such given path, permitting only very slight deviations on either side of such path, the two-plunger arrangement, illustrated in FIG. 4, is preferred.

The sensing head, according to the present invention, is preferably supported, with respect to the moving web W, in a position in which the desired normal path P of the edge W passes through space S intermediate the pair of plungers 10 and 10.

As noted above, each of the plungers 10 and 10 (FIG. 4), of the preferred two-plunger system, has associated with it its own pneumatic system 40 and 40', respectively. Pneumatic system 40' is identical in all respects to system 40 previously described. It will also be understood, however, that whileeach pneumatic system may have its own pressure source 41 and 41', respectively, as a practical matter it may be preferred to use the same pressure source for both systems.

When no web is present in the space S both plungers are in rest condition, namely, both plungers 10 and 10' are resting on the lower arm 32. In this condition the lower surfaces 14, 14' of the plungers are both in faceto-face contact with surface 33. In operation, with the edge W of a web W, advancing along path P intermediate the plungers l0 and 10' (FIG. 4), plunger 10 will be in rest condition, i.e., in contact with surface 33, permitting exhausting of the monitoring leg 50,, of system 40 to the atmosphere via passage 34' communicating with bore 15', while plunger 10 will be in a raised position, on top of web W, preventing exhausting to the atmosphere of the air in the monitoring leg 50,, of system 40. If the web edge W shifts laterally along a path indicated by arrow B (FIG. 1) into the region of plunger 10', the edge W thereof will contact the inclined portion 16' of plunger 10', lifting the latter. As the web W continues to shift in the direction of arrow B, it will lift the plunger 10 onto its upper surface thereby interrupting the flow of fluid between passage 16' and the bore 34'. This covering of the outlet opening 19' of passage 15 results in a build-up of pressure in space 22' which, in turn, results in the application of an increased force on the head 12' of plunger 10' urging the latter axially toward the upper surface of the web W, with which it is in contact, for sealing even better than before, the outlet opening 19' against escape of pressure fluid therefrom.

It will be understood that even where the web material is paper and even where such paper may be somewhat pervious to the pressure fluid used, a substantial build-up of pressure in space 22 or 22' will result, in response to covering of the corresponding outlet opening 19 or 19 with the paper web in the manner described above. This build-up of pressure will, of course, be immediately reflected back to, and be readily detected by, the corresponding differential pressure sensing means 44 or 44'.

Control means and 5' (FIG. 1) may each be a solenoid actuated valve. The solenoid valves are suitably energized via electric circuits 4 and 4', respectively, by the outputs, respectively of the differential pressure sensors 44 and 44' of the systems 40 and 40', respectively. The valves 5, 5' control the flow of pressure fluid, such as compressed air, from a suitable source (not shown) through conduits 4a and 4a, respectively, into chambers 3 and 3, respectively, at opposite sides of a double-acting piston 3a reciprocably received in a cylinder 6. Piston 3a is suitably connected, as by a rod, to a roller R which supports the web material, and is adapted to shift the latter in directions T.

In the preferred embodiment herein the solenoid of control means 5 is of the normally open type and is actuated, by system 40, into closed condition whenever the plunger is in its normal lifted condition (FIG. 4).

The solenoid of control means 5, on the other hand, is of the normally closed type and is actuated by system 40' into open position whenever the plunger 10' is in lifted condition.

With the edge W of web W in the position shown in FIG. 4, namely situated in path P, between the plungers 10 and 10', the normally open solenoid valve 5 is in activated condition, i.e., is closed, so that no further pressure fluid is admitted to chamber 3. Meanwhile normally closed valve 5 remains normally closed and the piston 3a remains at rest. In this condition of the web edge W plunger 10 is in lifted position with its outlet covered on the web surface, while plunger 10' is in rest position with its outlet uncovered on the surface 33 of lower arm 32. On the other hand, should the web edgge W shift in direction B, out of the path P, and out of engagement with plunger 10, outlet opening 19 will be uncovered so that now neither of the pair of plungers has its outlet opening covered. When this happens valve 5 is deactivated and returns to its normal open condition admitting pressure fluid to chamber 3 resulting in shifting of the web in direction B till edge W lifts plunger 10. Should the web edge W shift out of path P in the direction B thus lifting plunger 10, both plungers will be in lifted condition and both will have their outlet openings 19 and 19 respectively, covered by the surface of web W. ln that case solenoid 5 will be actuated into open condition and admit pressure fluid into chamber 3' so as to shift web W in direction B until edge W returns to path P.

It will be seen that even when no web is present under a plunger, since the pressure in the space 22 will be at least somewhat higher than atmospheric pressure, and since this pressure will act on the top surface 12 of the plunger, the latter will be urged toward surface 33 of the lower arm even while pressure fluid exhausts to the atmosphere through the bore 34. When, however, the web material has passed under the plunger and lifted the latter, the pressure in space 22 is greatly increased as a result of the web covering the outlet opening 19 of the bore 15 in the latter condition. The force with which the plunger is pressed against the surface of the web may be controlled by suitably adjusting the level of the system pressure at the source 41.

The force required to hold the plunger against the paper web, after the plunger has been lifted on to the surface of the web, will vary with the type of web, the web tension, the web material and the web speed. It will be obvious to those skilled in the art that the air pressure of the system may be adjusted so that sufficiently steady contact is maintained between the plunger and the surface of the web. Time delay means, such as time delay relays, well known to those skilled in the art, may be used in suitable circuitry to prevent brief intermittent surges, such as could result from web flutter, from disturbing the operation of the edge sensing apparatus described herein.

The differential pressure sensing means 44 may be of a type which produces an output signal in response to detection of a given pressure differential between the legs 50 and 50,, of the conduit means 42.

An edge sensing apparatus according to the present invention has been successfully constructed using air as the pressure medium.

By way of specific example, and without in any way intending to limit the scope of the invention a pair of aluminum plungers each approximately one-half inch long and 0.2808 inch in diameter were used in conjunction with a pair of chambers each approximately 0.2810 inches in diameter. No seals or gaskets of any kind were used to prevent the escape of air around the plungers. The plungers had internal bores 15, 15' of approximately 0.125 inches in diameter. With this sensing head incorporated in a two-plunger sensing system similar to the FIG. 1 system, a paper web was fed through the slot S at a speed, in the direction A, of approximately 1,000 feet per minute. A common air source (41 and 41') was used. The norminal air pressure at the source was approximately 1 pounds per square inch (A Fairchild-Hill, Stratos-Kendall, Model 65 Pressure Regulator was used to obtain the desired pressure at the source). Using a commercial pressure switch (A Fairchild Controls Faircon" Differential Pressure Switch, including a Pressure Sensor, Model No. PF-lOO-A and a Solid State Relay, Model No. SRFBA) as the differential pressure sensor means, a typical pressure change of 0.] pounds per square inch was detected when the edge W1. of the web entered under and interrupted the air flow through the corresponding one of the plungers.

It will be seen that the detection capability of apparatus, according to the present invention, will be essentially unaffected by variations in the air supply pressure.

It will also be seen that either the transverse position of the web or alternatively the transverse position of the sensing head 1 may be varied in response to the signals generated by the control means 5 and 5'.

Thus, in still a further embodiment of the present invention, the sensing head 1 may be mounted for movement (not shown) in transverse directions B and B. Suitable servo means, well known to those skilled in in the art, may be provided for maintaining the sensing head 1 in a position, with respect to the edge W of the web, such that the latter edge is always located between head 1 suitably mounted for movement in direction B 10 and B instead of to the roller R, the sensing head 1 can be made to automatically follow the edge W, of the web whenever the latter shifts transversely with respect to the direction of advance of the web.

Thus it will be seen that the present invention may be employed to provide a control signal to regulate apparatus for performing various functions, as for pure indication or for control of apparatus that may or may not affect the position of the edge of which the position is detected.

It should be clearly understood that while the description, for the sake of simplicity, has referred to air as the pressure fluid the invention is not so limited. Thus, the pressure fluid may be any gas. However, ordinary compressed air is entirely satisfactory and as a practical matter is preferred.

The invented structure, as exemplified by the embodiments described in detail herein, offers the importarit advantage of being capable of accurately and reliably detecting lateral shift of the edge of a web of even a delicate material such as paper and even while the latter is moving at a high rate of speed.

The apparatus according to the present invention overcomes, in a very simple and economical manner, the difficulties encountered by the prior art devices. The sensing system, according to the present invention, has the additional advantage of always being purged positively thus eliminating all possibility of being clogged by dust or other pollutants in the atmosphere. Furthermore, the arrangement according to the present invention operates satisfactorily on webs of different caliper and requires, in fact, no readjustment should the caliper of the web change or a web of different caliper be encountered. While it has been described herein as being particularly suitable for use with paper it will be understood that the present invention may be used with any web material which is at least partly impervious to the flow of air or other gaseous medium, therethrough.

It will thus be seen that the objects set forth above, and those made apparent from the preceding description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter oflanguage, might be said to fall therebetween.

1. In an apparatus for detecting the traverse of an edge of a moving web of sheet material along a given path, in combination:

a movable feeler member having spaced first and second portions, and a passage for pressure fluid extending between said first and second portions, said passage having an outlet opening in said first portion, and said feeler member being normally in a first position in which said first portion thereof extends into said path and said outlet opening is uncovered;

actuating means associated with said feeler member adapted to'be engaged by the edge of the moving web for displacing said member out of said path in response to the edge of the web moving along said path and for placing said member into a second position in which said first portion thereof engages a surface of the web, said oulet opening being positioned such as to be covered by the web surface when said first portion of said feeler member is engaged thereby;

conduit means adapted to be connected to a source of pressure fluid and communicating with said passage, said pressure fluid flowing through said passage and out said outlet opening when the latter is uncovered by the web surface;

means cooperating with said feeler member for enabling a build-up of fluid pressure against said second portion of said feeler member when said outlet opening is covered by the web, thereby to cause said first portion of said feeler member to be pressed against the web surface so as to substantially seal said'outlet opening against escape of pressure fluid therefrom; and

pressure sensing means associated with said conduit means for detecting said build-up of fluid pressure therein.

2. Apparatus according to claim 1, wherein said feeler member is a substantially cylindrical plunger, said first and second portions being the opposite end portions, respectively, of said plunger; and

said passage extending in substantially axial direction through said plunger.

3. Apparatus according to claim 2, wherein said first end portion of said plunger includes said actuating means, the latter comprising an inclined surface portion facing generally toward the leading edge, along said given path, of a web, and adapted to be engaged by such leading edge for lifting said plunger out of said path in response to movement of the edge of the web under said plunger.

4. Apparatus according to claim 1, further comprising support means defining therein a chamber spaced above and opening in the direction of the plane of the web and adapted to receive said feeler member therein for relative sliding movement into and out of said path.

5. Apparatus according to claim 4, wherein said chamber communicates with said conduit means and said passage has an inlet opening in said portion of said feeler member communicating with the interior of said chamber.

6. Apparatus according to claim 4, further comprising a web guide surface means spaced from and facing toward the opening of said chamber, said feeler member being freely movable in said chamber between said first position thereof in which it engages said web I guide surface means and said second position thereof in which it engages the surface of a web supported on said surface means, said surface means including a throughbore in registry with said passage for exhausting pressure fluid from said chamber to the atmosphere whenever said feeler member is in said first position thereof.

7. Apparatus according to claim 6 further comprising a second said chamber provided in said support means adjacent the first mentioned chamber, a second said feeler member received in said second chamber, and second said conduit means communicating with said second chamber and adapted to be connected with a source of pressure fluid for building up fluid pressure against said second portion of said second feeler member when the outlet opening thereof is covered by the web.

8. Apparatus according to claim 1, wherein said first portion of said feeler member includes a planar surface portion surrounding said outlet opening for substantially sealingly engaging the surface of the web material when the latter is positioned under the feeler member.

9. Apparatus for maintaining the edge of a longitudinally advancing web of material substantially in a predetermined longitudinal path, comprising, in combination:

a source of pressure fluid;

first and second conduit means communicating with said source of pressure fluid; first pressure sensing means cooperating with said first conduit means and second pressure sensing means cooperating with said second conduit means for respectively, providing signals in response to detection of a pressure change of predetermined magnitude in the respective ones of said conduit means; web guide means, located along said predetermined path, including a lower guide portion and a spaced upper portion defining with said lower portion a slot adapted to receive the edge portion of the moving web, said lower portion having a top surface for supporting the web when the latter extends into said slot and said upper portion defining a pair of adjacent chambers together straddling said predetermined path and each opening toward said top surface of said lower portion, said chamber communicating, respectively, with corresponding ones of said first and second conduit means; I

a pair of movable feeler members respectively slidably received in said chambers, said feeler members each having spaced first and second end portions and a passage for pressure fluid extending between said first and second end portions, each said passage having an inlet opening in said second end portion and an outlet opening in said first end portion thereof and communicating with the corresponding chamber, and said feeler members being slidable between a first position in which said first portion thereof extends into said predetermined path and said outlet opening is uncovered and a second position in which said first portion engages the surface of the web and said outlet opening is covered by the web surface;

a pair of actuating means respectively associated with said first portion of each of said feeler members for moving the respective feeler member from said first into said second position thereof in response to an edge of the web material engaging the corresponding actuating means, said actuating means being adapted to lift the corresponding feeler member onto the surface of the web material in response to movement of the web thereunder, whereby said outlet opening of the lifted feeler member will be at least partially covered by such web material resulting in a build-up of pressure in the corresponding one of said conduit means.

10. Apparatus according to claim 9 wherein said web edge is normally located along said predetermined path intermediate the pair of feeler members so that one of said feeler members is normally in said first position thereof, with its outlet opening uncovered, and the other of said feeler members is normally in said second position thereof with its outlet opening covered by the web surface, the conduit means communicating with said one feeler member normally discharging through said outlet opening thereof to the atmosphere and the conduit means communicating with said other feeler member normally having pressure built-up therein, said apparatus further comprising operating means, operatively connected with said pressure sensing means, for operating on said web material in response to a signal from either of said pressure sensor means indicating a change in the normal position of either of said feeler members in response to lateral shifting of the edge of the web material out of said predetermined path between the pair of feeler members.

11. Apparatus according to claim 10 wherein each of said conduit means includes a monitoring conduit communicating at one end thereof with said source of pressure fluid and at the other end thereof with the respective one of said chambers; and a reference conduit communicating at one end thereof with said source of pressure fluid and at the other end thereof with the atmosphere; each said pressure sensor means communicating with intermediate portions, respectively, of said monitor and reference conduits of the correspond ing one of said conduit means for sensing a change in pressure of the pressure fluid in said monitoring conduit of the corresponding conduit means with respect to the pressure in said reference conduit thereof in response to the web edge shifting out of said predetermined path toward and beyond one or the other of said feeler members so as to either cover the outlet opening of said one feeler member on to uncover the outlet opening of said other feeler member.

12. In an apparatus for detecting movement of an edge of sheet material along a given path in combination:

a movable feeler member positioned for movement into and out of said path, said feeler member being adapted to be lifted by the edge of the sheet material onto and into engagement with the surface of the sheet material in response to said edge moving along said path into the region of said feeler member;

a conduit in said feeler member having an outlet opening toward said path and adapted to be covered by the surface of the sheet material when the latter is in said region;

pressure-fluid means cooperating with said feeler member for discharging through said conduit when no sheet material is present in said region so 

1. In an apparatus for detecting the traverse of an edge of a moving web of sheet material along a given path, in combination: a movable feeler member having spaced first and seCond portions, and a passage for pressure fluid extending between said first and second portions, said passage having an outlet opening in said first portion, and said feeler member being normally in a first position in which said first portion thereof extends into said path and said outlet opening is uncovered; actuating means associated with said feeler member adapted to be engaged by the edge of the moving web for displacing said member out of said path in response to the edge of the web moving along said path and for placing said member into a second position in which said first portion thereof engages a surface of the web, said outlet opening being positioned such as to be covered by the web surface when said first portion of said feeler member is engaged thereby; conduit means adapted to be connected to a source of pressure fluid and communicating with said passage, said pressure fluid flowing through said passage and out said outlet opening when the latter is uncovered by the web surface; means cooperating with said feeler member for enabling a buildup of fluid pressure against said second portion of said feeler member when said outlet opening is covered by the web, thereby to cause said first portion of said feeler member to be pressed against the web surface so as to substantially seal said outlet opening against escape of pressure fluid therefrom; and pressure sensing means associated with said conduit means for detecting said build-up of fluid pressure therein.
 2. Apparatus according to claim 1, wherein said feeler member is a substantially cylindrical plunger, said first and second portions being the opposite end portions, respectively, of said plunger; and said passage extending in substantially axial direction through said plunger.
 3. Apparatus according to claim 2, wherein said first end portion of said plunger includes said actuating means, the latter comprising an inclined surface portion facing generally toward the leading edge, along said given path, of a web, and adapted to be engaged by such leading edge for lifting said plunger out of said path in response to movement of the edge of the web under said plunger.
 4. Apparatus according to claim 1, further comprising support means defining therein a chamber spaced above and opening in the direction of the plane of the web and adapted to receive said feeler member therein for relative sliding movement into and out of said path.
 5. Apparatus according to claim 4, wherein said chamber communicates with said conduit means and said passage has an inlet opening in said portion of said feeler member communicating with the interior of said chamber.
 6. Apparatus according to claim 4, further comprising a web guide surface means spaced from and facing toward the opening of said chamber, said feeler member being freely movable in said chamber between said first position thereof in which it engages said web guide surface means and said second position thereof in which it engages the surface of a web supported on said surface means, said surface means including a through-bore in registry with said passage for exhausting pressure fluid from said chamber to the atmosphere whenever said feeler member is in said first position thereof.
 7. Apparatus according to claim 6 further comprising a second said chamber provided in said support means adjacent the first mentioned chamber, a second said feeler member received in said second chamber, and second said conduit means communicating with said second chamber and adapted to be connected with a source of pressure fluid for building up fluid pressure against said second portion of said second feeler member when the outlet opening thereof is covered by the web.
 8. Apparatus according to claim 1, wherein said first portion of said feeler member includes a planar surface portion surrounding said outlet opening for substantially sealingly engaging the surface of the web material when the latter is positioned under the feeler member.
 9. Apparatus for maintaining the edge of a longitudinally advancing web of material substantially in a predetermined longitudinal path, comprising, in combination: a source of pressure fluid; first and second conduit means communicating with said source of pressure fluid; first pressure sensing means cooperating with said first conduit means and second pressure sensing means cooperating with said second conduit means for respectively, providing signals in response to detection of a pressure change of predetermined magnitude in the respective ones of said conduit means; web guide means, located along said predetermined path, including a lower guide portion and a spaced upper portion defining with said lower portion a slot adapted to receive the edge portion of the moving web, said lower portion having a top surface for supporting the web when the latter extends into said slot and said upper portion defining a pair of adjacent chambers together straddling said predetermined path and each opening toward said top surface of said lower portion, said chambers communicating, respectively, with corresponding ones of said first and second conduit means; a pair of movable feeler members respectively slidably received in said chambers, said feeler members each having spaced first and second end portions and a passage for pressure fluid extending between said first and second end portions, each said passage having an inlet opening in said second end portion and an outlet opening in said first end portion thereof and communicating with the corresponding chamber, and said feeler members being slidable between a first position in which said first portion thereof extends into said predetermined path and said outlet opening is uncovered and a second position in which said first portion engages the surface of the web and said outlet opening is covered by the web surface; a pair of actuating means respectively associated with said first portion of each of said feeler members for moving the respective feeler member from said first into said second position thereof in response to an edge of the web material engaging the corresponding actuating means, said actuating means being adapted to lift the corresponding feeler member onto the surface of the web material in response to movement of the web thereunder, whereby said outlet opening of the lifted feeler member will be at least partially covered by such web material resulting in a build-up of pressure in the corresponding one of said conduit means.
 10. Apparatus according to claim 9 wherein said web edge is normally located along said predetermined path intermediate the pair of feeler members so that one of said feeler members is normally in said first position thereof, with its outlet opening uncovered, and the other of said feeler members is normally in said second position thereof with its outlet opening covered by the web surface, the conduit means communicating with said one feeler member normally discharging through said outlet opening thereof to the atmosphere and the conduit means communicating with said other feeler member normally having pressure built-up therein, said apparatus further comprising operating means, operatively connected with said pressure sensing means, for operating on said web material in response to a signal from either of said pressure sensor means indicating a change in the normal position of either of said feeler members in response to lateral shifting of the edge of the web material out of said predetermined path between the pair of feeler members.
 11. Apparatus according to claim 10 wherein each of said conduit means includes a monitoring conduit communicating at one end thereof with said source of pressure fluid and at the other end thereof with the respective one of said chambers; and a reference conduit communicating at one end thereof with said source of pressure fluid and at the other end thereof with the atmosphere; each said pressure sensor means communicating with intermediate portions, respectively, of said monitor and reference conduits of the corresponding one of said conduit means for sensing a change in pressure of the pressure fluid in said monitoring conduit of the corresponding conduit means with respect to the pressure in said reference conduit thereof in response to the web edge shifting out of said predetermined path toward and beyond one or the other of said feeler members so as to either cover the outlet opening of said one feeler member on to uncover the outlet opening of said other feeler member.
 12. In an apparatus for detecting movement of an edge of sheet material along a given path in combination: a movable feeler member positioned for movement into and out of said path, said feeler member being adapted to be lifted by the edge of the sheet material onto and into engagement with the surface of the sheet material in response to said edge moving along said path into the region of said feeler member; a conduit in said feeler member having an outlet opening toward said path and adapted to be covered by the surface of the sheet material when the latter is in said region; pressure-fluid means cooperating with said feeler member for discharging through said conduit when no sheet material is present in said region so that said outlet opening is uncovered, and for building up pressure behind said feeler member for urging the latter against the sheet material when sheet material is in said region and covers said outlet opening; and means cooperating with said pressure-fluid means for detecting said build-up of pressure. 